The present invention relates to isolated power converters, and in particular to voltage sensing for isolated power converters.
Isolated converters are used to provide isolated power to a load. This isolation is generally provided through the use of an isolation transformer between an input power stage and an output power stage. This allows energy to be transferred from the input stage to the output stage while allowing each stage to be grounded to a different potential.
The voltage in the output stage needs to be controlled in order to provide proper voltage to the load. Because the output stage receives power from the input stage, the output voltage is controlled by controlling the flow of energy from the input source. Therefore, measurements must be made in the output stage and used to control the input stage. This becomes a problem due to the isolation between the two stages. Given that the ground potential for each of the stages are often, by design, at different potentials, voltages in the output stage cannot be directly compared to voltages in the input stage. Thus, in some designs, the output voltage must be brought back across the isolation barrier in order to be used for the controls for the input stage. This has been accomplished in the past through the use of isolated operational amplifiers, additional feedback windings on the isolation transformer, or digitization of the voltage along with feedback through optical isolation. All of these methods have drawbacks such as unreliability, added complexity and added cost.